The field of the invention is auxiliary battery systems for supplying 28 volts Direct Current (DC) power to aircraft.
Direct current (DC) power systems on small and medium sized aircraft are typically 12, 24, or 28 volts. An on-board battery of the corresponding voltage is used in the aircraft for starting and emergency power. During ground maintenance operations, it is desirable to supply an auxiliary source of power so that the on-board batteries are not depleted. On medium sized aircraft, for example twin engine aircraft and small business jets, a receptacle is provided for this purpose.
The auxiliary source of power may be either an engine generator set or battery pack. Using a battery pack is preferred in most small to medium sized applications because of low maintenance requirements and freedom from noise and vibration. The battery pack is usually composed of several cells or batteries of lower voltages externally connected in series to achieve the desired voltage for the battery pack.
For 12 and 24 volt systems, commercial batteries are readily available as these voltages are commonly used in automotive, truck and other industrial applications. Prior battery packs for 28 volt auxiliary aircraft power, however, were usually composed of a bank of fourteen lead acid cells of 2 volts each. Such battery packs are generally acceptable, but are relatively expensive, owing to limited availability of individual 2 volt cells and the additional wiring needed to connect them together.
Additionally, chargers for the prior 28 volt battery packs also have limited availability, since they have applicability only to aircraft systems, are relatively expensive, and are predominantly of the trickle charge variety as opposed to automatic shutdown type chargers. Chargers of the automatic shutdown type are preferred in those applications of battery packs for supplying auxiliary aircraft power were used of the battery pack is sporadic. Under those circumstances, it is desirable to charge the battery pack fully at a normal rate and then to have the charger shut down until manually restarted, which is exactly the operation provided by an automatic shutdown type charger. Using trickle chargers in such applications may damage the battery pack if left unattended for long periods by overcharging the battery pack or causing excessive loss of electrolyte.